Ongoing water seepage of up to 3,600 litres per minute complicates SLBC tunnel rescue efforts, making slush removal a major challenge.
Domalapenta: The SLBC tunnel had been experiencing seepage from the very beginning of the start of the project and on Saturday, the pressure of water in the rocks above was just too much for the structures being put in place to face.
Even as sections of large cement concrete arcs were being placed along the walls of the tunnel, a ‘regular’ and ‘normal’ amount of seepage of around some 2,000 to 3,000 litre per miniute, something that is dealt with in a routine manner, suddenly increased.
The pressure was so much that the cement concrete rings that were being placed on the tunnel walls collapsed, and sections of the tunnel in a stretch that was just dug, gave way,” an irrigation department engineer A. Srinu said.
“Even today, we are having some 3,600 litres of water coming per minute and this is making things difficult,” he said.
A senior functionary of Jaiprakash Associates, Pradeep, said though things may seem normal in terms of events such as ‘normal’ seepage, “everyday is a new day.”
The continuing inflows into the tunnel are proving to be one of the biggest challenges for the rescue efforts officials overseeing rescue efforts said. “If the water reduces, then the slush may compact and that might help in crossing over it,” an official said.
Pradeep said the slush level was some 15 feet high near the collapsed section where a large section of the 200 metres long TBM now lies buried. The tunnel height is around 32 feet which means a good part of the TBM is under the fallen rock and soil.
“Dewatering is not a problem, we deal with it every day, but getting rid of the slush will be challenge,” a senior irrigation department engineer said. One large dewatering pump has been procured and one more is on the way, the official added.
According to Venkateswarulu, the forest divisional officer in Mannanur village, which marks the beginning of the Amrabad tiger reserve under which the tunnelling is going on, on Saturday, officials checked the spot overground, the location where the tunnel boring machine got buried, to look at the possibility of drilling a hole from the to try and reach out to the trapped workers.
“Though a tiger reserve, this time we were ready to allow drilling, even laying of a road for the machinery to rescue the workers, but it was found that the tunnel is at a depth of around 450 metres of solid rock and the idea was dropped at the exploratory stage,” he said.
Srinu said a seasonal stream passes very close to that location overground and it is quite possible that water percolating down may have formed an aquifer of sorts and the pressure from it when the TBM reached the spot underground, possibly resulted in the overburden collapsing.
